1. Field of the Invention
The present invention relates to a steering shaft assembly for automotive vehicles, and more particularly to a steering shaft assembly of the telescopic type adjustable in its axial direction.
2. Description of the Prior Art
Disclosed in Japanese Utility Model Laid-open Publication 56(1981)-27175 is a steering shaft assembly of the telescopic type which comprises a lower shaft operatively connected to a steering gear box, an upper shaft telescopically connected to the lower shaft for axial adjustment in such a manner as to restrict relative rotation to the lower shaft and provided thereon with a steering wheel, and a lock mechanism for releasably fastening the upper shaft to the lower shaft at an adjusted position. In the steering shaft assembly, the upper shaft is in the form of a hollow shaft having a lower end portion formed as a pair of diametrically opposed deformable portions for engagement with an outer periphery of the lower shaft, and the lock mechanism is comprised of a tubular fastening member threaded over the hollow upper shaft. The tubular fastening member is formed with a tapered female screw portion in engagement with tapered male screws formed on the deformable portions of the hollow upper shaft. When the tubular fastening member is rotated by operation of a manual lever connected thereto to radially inwardly tighten the deformable portions of the hollow upper shaft to the outer periphery of the lower shaft, the upper shaft is locked at an adjusted position.
In this kind of steering shaft assemblies, it is desired to provide a shock absorbing mechanism for absorbing a forward impact applied in excess to the steering wheel. In the steering shaft assembly described above, it is, however, difficult to provide such a shock absorbing mechanism in combination with the lock mechanism. If the shock absorbing mechanism was provided separately from the lock mechanism, the steering shaft assembly would become complicated in construction.